1. Field of the Invention
The present invention relates to a solid-state image pickup device, a method for manufacturing the same, and an image pickup apparatus.
2. Description of the Related Art
A semiconductor image sensor has a plurality of pixels functioning as photoelectric conversion portions. As this semiconductor image sensor, for example, there may be mentioned a CMOS sensor in which MOS transistors are used as elements which selectively read out a plurality of pixels and a charge coupled device (CCD) in which charges are transferred in a silicon substrate and are then read out, and these two image sensors are each a semiconductor device which reads out signals of pixels. In recent years, because of features of the CMOS sensor, such as low voltage, low power consumption, and multifunctionality, much attention has been paid thereto as an image pickup element, such as a mobile phone camera, a digital still camera, and a digital video camera, and hence the range of the use of the CMOS sensor has been increased.
In addition, as a color image sensor, a technique has been generally used in which a color filter having, for example, three types of colors RGB (RGB Bayer arrangement is commonly used) is formed in each pixel, and spatial color separation is performed. According to this technique, when spectral characteristics of a color filter are appropriately adjusted, superior color reproduction can be achieved. However, since light absorption by the color filter itself is not small, there has been a fundamental problem in that light incident on the image sensor may not be sufficiently effectively utilized.
In addition, since spatial color separation is performed, pixels of the image sensor may not be effectively used. For example, when the number of green pixels is small, the resolution of luminance signals is degraded, and when the number of red and/or blue pixels is small, the resolution of color signals is degraded, that is, false color signals are disadvantageously generated.
Furthermore, concomitant with a reduction in size of the image sensor and an increase in number of pixels thereof, recently, the cell size of one pixel has been reduced to 2.0 μm square or less. Accordingly, the area and the volume per one pixel are naturally reduced, and as a result, the amount of saturation signals and the sensitivity are decreased, so that the image quality is degraded. Hence, when R/G/G signals can be obtained by one pixel or two to three pixels without reducing the cell size, while the sensitivity and the amount of saturation signals are each maintained at a predetermined level, the spatial luminance and the chroma resolution can be maintained.
As a method for solving the above problem, in recent years, an image sensor using a multilayer organic photoelectric conversion film has been developed (for example, see Japanese Unexamined Patent Application Publication No. 2003-234460). As shown in FIG. 9, an organic photoelectric conversion film 126 having a sensitivity to blue (B), an organic photoelectric conversion film 128 having a sensitivity to green (G), and an organic photoelectric conversion film 130 having a sensitivity to red (R) are sequentially laminated to each other. According to the image sensor described above, by the above structure, B/G/R signals can be separately obtained from one pixel, and the sensitivity can be improved.
On the other hand, a device has been realized in which only one organic photoelectric conversion film is formed to extract one color signal therefrom, and two color signals are extracted by silicon (Si) bulk spectroscopy (for example, see Japanese Unexamined Patent Application Publication No. 2005-303266). In addition, the inventors of the present invention have proposed, by using the structure of a whole-area-open-type CMOS image sensor (or also referred to as “back-illuminated CMOS image sensor”), a structure capable of improving the sensitivity and color reproduction (for example, see Japanese Unexamined Patent Application Publication No. 2008-258474).
The structure of one of these related techniques is shown in FIGS. 10A to 11B by way of example.
As shown in FIGS. 10A and 10B, for example, although lower electrodes 141 are independently formed for respective pixels 121, an organic photoelectric conversion layer 144, a blocking film 146 for decreasing a dark current, and the like are not separated for the respective pixels 121.
Hence, optical factors and electrical factors between the pixels 121 degrade spatial resolution capability and are partially responsible for color mixture. As the optical factors, for example, a phenomenon in which light incident on one pixel directly leaks in an adjacent pixel thereto may be mentioned, and as the electrical factors, for example, a phenomenon in which carriers generated by photoelectric conversion of light incident on one pixel leak in an adjacent pixel thereto may be mentioned.
When the organic photoelectric conversion film 144 has a small thickness, since a voltage is applied between transparent electrodes, influences of the above-described optical factors and electrical factors are relatively small. However, in order to improve the spectral characteristics, hereinafter, the thickness of the organic photoelectric conversion film 144 tends to be increased. In this case, it becomes more difficult to ignore problems, such as occurrence of color mixture and degradation in spatial resolution capability, and hence improvements thereof have been strongly desired.
As one example of a method to suppress the color mixture and the degradation in spatial resolution capability, as shown in FIG. 11A, the structure has been disclosed in which a first electrode 162, a buffer layer 163, a photoelectric conversion layer 164, and a second electrode 165 are provided on a substrate 161 and are isolated for each element (for example, see Japanese Unexamined Patent Application Publication No. 2008-53252). In addition, as shown in FIG. 11B, the structure has been disclosed in which a first electrode 162, a buffer layer 163, and a photoelectric conversion layer 164 are provided on a substrate 161 and are isolated for each pixel and in which an electrical insulating portion 169 is formed at an isolation portion (for example, see Japanese Unexamined Patent Application Publication No. 2008-53252). As a method for isolating the photoelectrical conversion layer 164 and the buffer layer 163 for each element, etching or lift-off has been used. However, in the etching, degradation in characteristics caused by damage and control of selection ratio are problems, and in the lift-off, for example, pattern accuracy, fine pattern handling, and dust generation are problems. Furthermore, although electrical isolation has been proposed, optical isolation to directly avoid the color mixture has not been disclosed, and the effect of preventing the color mixture has not been sufficient.